Bypass Tube and electric water pumps

["James J." <m1garand@speakeasy.net>]

All,
   The little tube that runs from the back side of the water-pump to 
the small tube on the thermostat cover, called the bypass tube:  As far 
as I can tell, that allows the pump to circulate a little water through 
the block and heads prior to the thermostat opening.  Or is the 
circulation just a way of keeping the pump from cavitating until the 
thermostat opens?  Is that correct?  If so, is it necessary?
   I ask because many of the electric water pumps don't turn on until 
the water gets to a certain temp.  Also, if you use a remote water pump 
instead of the belt-driven one, it is usualy in a location where it 
would take some really clever rigging to get it to provide that 
circulation function prior to the thermostat opening, so I'm asking if 
anyone knows what the bypass tube really does, and if it is a necessary 
function.

Thanks.
James J.

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